The Shushtar Hydraulic System in the island city of Shushtar is a complex irrigation system that dates back to the time of the Achaemenid king Darius the Great in the 5th century BCE. Described by UNESCO “as a masterpiece of creative genius”, the Shushtar Hydraulic System involved the creation of a diversion canal on the river Karun to form a moat around the city, over which bridges and gates were built to keep away unwanted visitors